Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1246 PM EST Sun Jan 05 2020
Valid 12Z Wed Jan 08 2020 - 12Z Sun Jan 12 2020
...Heavy Rain Threat from the Lower Mississippi to Ohio Valleys
Fri-Sat...
...Overview/Guidance Assessment...
Guidance continues to advertise an amplified mean trough aloft for
the western U.S., between ridges over the east-central Pacific and
the Southeast U.S.. The Climate Prediction Center 8-14 Day
forecast still suggests some variation of this pattern may persist
well beyond the end of the medium range period. Evolution aloft
and surface features will lead to a heavy rain threat most likely
from the Lower Mississippi Valley through the Tennessee Valley and
Ohio Valley. Teleconnections relative to the positive height
anomaly center which multi-day means show near or offshore the
East Coast later in the period also target this area for greatest
precipitation potential. Meanwhile North Pacific energy feeding
into the mean trough will bring episodes of enhanced precipitation
with best focus over the Pacific Northwest.
Forecast spread at medium range time scales has decreased since
yesterday, bolstering forecast confidence. GEFS/NAEFS/ECMWF
ensembles are now more in line with the ECMWF/UKMET/Canadian and
GFS, now that the 12 UTC GFS has trended to a less progressive
CONUS solution late week to next weekend. Favor a guidance
composite of these solutions that maintains good WPC continuity.
...Weather Highlights/Threats...
A lead low/system tracking off the New England coast Wed will
strengthen as it heads into the Canadian Maritimes and support
wrapback snows and a period of breezy conditions in its wake.
Upstream, a northern Plains to eastern Canadian system Wed-Fri
will wrap some moderately heavy snows into a cooled northern
Plains/Upper Midwest/Great Lakes.
Confidence is increasing for the potential of a heavy rainfall
event from the Lower Mississippi Valley into the Tennessee Valley
and Ohio Valley late this week into the weekend. The cold front
trailing from late week Plains-eastern Canada system will have
several embedded waves and may progress fairly slowly for a time
while awaiting upstream western energy aloft. Two or three days of
Gulf inflow ahead of this wavy front would provide considerable
moisture to enhance rainfall amounts and some embedded convection
is possible. This area encompasses some locations that recently
received significant rainfall, so effects from this upcoming event
will require close monitoring. There is a growing a signal for
wintry precipitation on the northern periphery of the moisture
shield, and significant accumulation probabilities are trending up.
Over the West, still expect highest totals of rain/mountain snow
over the Pacific Northwest coast/northwest corner of California as
well as the Cascades, with a secondary maximum over the northern
Rockies. Some moisture will extend southeastward but with lighter
amounts in most cases. Heaviest precipitation should occur from
Fri into the weekend, though amounts are likely not to be extreme
given fairly modest precipitable water anomalies.
Schichtel
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml